Railway vehicles traditionally use a braking system wherein a brake shoe is mounted toward opposed ends of a brake beam and is selectively moved against a wheel surface of the vehicle to provide a retarding force. In most railway braking systems, the brake shoe is detachably mounted to a brake head used to locate the brake shoe and provide the braking force to the brake shoe.
A typical brake shoe includes a friction element carried by an arcuately configured metal backing plate. A keybridge extends outwardly from the backing plate and defines a pair of longitudinally spaced and generally aligned openings. The brake shoe keybridge is insertable between longitudinally spaced carrier lugs transversely extending across and formed as part of the brake head. The carrier lugs serve to support the brake shoe backing plate and inhibit the brake shoe from longitudinally shifting during a braking action. The brake head has certain standardized features and dimensions as established by the Mechanical Division of the Association of American Railroads (AAR) to allow interchangeability between brake shoes and brake beams made by different manufacturers.
The brake shoe keybridge area of the backing plate is formed in such a way that it is adapted to protrude into or intersect, at or near the longitudinal center of the brake head, with a longitudinally elongated keyway or channel formed in the brake head. An elongated brake shoe key, also of standard design, is manually insertable downwardly through the keyway or channel, behind the carrier lugs, and is designed to pass through the aligned openings in the brake shoe keybridge. By this insertion, the brake shoe is detachably assembled to each brake head.
Assembly of the brake shoe to the brake head by means of the brake shoe key has occasionally proved troublesome. The location of the brake head on the railcar makes proper insertion of the brake shoe key, used to hold the brake shoe and brake head in operable combination, awkward. Additionally, and because railroads operate on a round-the clock schedule, replacement of the brake shoes, requiring proper insertion of the brake shoe key to hold the replaced brake shoe and brake head in operable combination, must occasionally happen during periods of sever weather and at night. Accordingly, the person charged with replacement of the brake shoes is sometimes hurried to complete their task.
The design of the typical brake shoe, whether cast or formulated, also complicates proper insertion of the brake shoe key to hold the brake shoe and brake head in operable combination. That is, a conventional brake shoe has internal areas that can interfere with proper insertion of the brake shoe key into operable combination with the keybridge on the brake shoe. More specifically, the carrier lug arranged toward the longitudinal center of the brake head can interfere with endwise movement and proper insertion of the elongated key into the brake head. Such interference with key movement can cause the person inserting the key to erroneously and/or mistakenly believe the key has locked the brake shoe to the brake head. Since such interference, however, does not permit adequate insertion of the key, the brake shoe is not securely attached to the brake head. When a brake shoe key is not fully inserted, vibration of the railcar coupled with interaction between the shoe and brake head have a tendency to walk the brake key upward to further loosen the assembly. With a loose assembly, the brake shoe will not properly be held in place, will not likely contact the wheel correctly, and most likely the brake shoe will fall off. If the brake shoe falls off, the brake head will contact the wheel during braking causing possible detrimental damage to the both the wheel and brake head.
Thus, there is a continuing need and desire for a brake head which promotes passage of the brake shoe key through the keyway and into proper combination with the brake shoe keybridge so as to affect proper securement of the brake shoe key and brake head.